Laser processing apparatus

ABSTRACT

A laser processing apparatus includes a cassette table for placing thereon a cassette in which a plurality of workpieces are accommodated, a carrying-out unit for carrying out the workpiece from the cassette placed on the cassette table, an X-axis direction moving unit for processing feed of a chuck table in the X-axis direction, a Y-axis direction moving unit for indexing feed of the chuck table in a Y-axis direction orthogonal to the X-axis direction, and a laser beam applying unit having a focusing unit for applying a laser beam to the workpiece held on the chuck table.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a laser processing apparatus which iscapable of efficiently processing a plate-shaped workpiece such as awafer, thereby enhancing productivity.

Description of the Related Art

A wafer formed with devices such as integrated circuits (ICs) or largescale integrations (LSIs) on a front surface thereof partitioned bydivision lines is processed along the division lines by a laserprocessing apparatus, and is divided into individual device chips, whichare used for electrical apparatuses such as personal computers, mobilephones, and television sets.

As the laser processing apparatus, there has been known one thatincludes, at least, a cassette table for placing thereon a cassette inwhich a plurality of workpieces are accommodated, carrying-out means forcarrying out the wafer from the cassette placed on the cassette table,temporary placing means for temporarily placing the wafer carried out bythe carrying-out means, carrying means for carrying the wafer from thetemporary placing means to a chuck table, imaging means for imaging thewafer held on the chuck table and detecting a region to be processed,and laser beam applying means including a focusing unit for applying alaser beam to the wafer held on the chuck table (see, for example,Japanese Patent Laid-Open No. 2004-022936). In the laser processingapparatus, the wafer can be processed with high accuracy byreciprocating the chuck table, which holds the wafer, in relation to thelaser beam applying means.

SUMMARY OF THE INVENTION

According to the aforementioned laser processing apparatus, a wafer as aworkpiece can be processed with high accuracy. However, in theabove-mentioned related art, the moving base to which the chuck tablewith the wafer supported thereon is formed from stainless steel(specific gravity: 7.9). Therefore, there is a problem thathigh-velocity movement of the chuck table is restricted by the inertialforce at the time of reciprocating the moving base in relation to thelaser beam applying means, so that it is impossible to process the waferefficiently.

Accordingly, it is an object of the present invention to provide a laserprocessing apparatus capable of efficient processing of a workpieceincluding a wafer.

In accordance with an aspect of the present invention, there is provideda laser processing apparatus for processing a plate-shaped workpiece byapplying a laser beam to the workpiece, the laser processing apparatusincluding a cassette table for placing thereon a cassette in which aplurality of workpieces are accommodated, carrying-out means forcarrying out the workpiece from the cassette placed on the cassettetable, temporary placing means for temporarily placing the workpiececarried out by the carrying-out means, carrying means for carrying theworkpiece from the temporary placing means to a chuck table, imagingmeans for detecting a region to be processed of the workpiece held onthe chuck table, X-axis direction moving means for processing feed ofthe chuck table in an X-axis direction, Y-axis direction moving meansfor indexing feed of the chuck table in a Y-axis direction orthogonal tothe X-axis direction, and laser beam applying means including a focusingunit for applying a laser beam to the workpiece held on the chuck table.The X-axis direction moving means includes a moving base for supportingthe chuck table, an X-axis table having an X-axis guide rail for guidingthe moving base in the X-axis direction, and a drive source for movingthe moving base. The Y-axis direction moving means includes a Y-axisguide rail for guiding the X-axis table in the Y-axis direction, and adrive source for moving the X-axis table. The moving base is formed froma carbon fiber-reinforced plastic.

According to the laser processing apparatus of the present invention,the inertial force attendant on the reciprocating movement is reduced to¼ times that in the case of the conventional moving base formed fromstainless steel. For example, while the moving velocity at the time ofputting the conventional moving base into high-velocity movement withina range limited by the size, of the apparatus is 1,000 mm/second atmaximum, the moving velocity in the case of the moving base in thepresent invention can be raised to 2,000 mm/second, or approximately twotimes that in the conventional case. For this reason, it is possible,according to the present invention, to laser process the waferefficiently.

The above and other objects, features and advantages of the presentinvention and the manner of realizing them will become more apparent,and the invention itself will best be understood from a study of thefollowing description and appended claim with reference to the attacheddrawings showing a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general perspective view of a laser processing apparatusaccording to an embodiment of the present invention;

FIG. 2 is an exploded perspective view for separately explaining mainportions of the laser processing apparatus depicted in FIG. 1;

FIG. 3 is a perspective view depicting a chuck table and a moving baseof the laser processing apparatus depicted in FIG. 1;

FIGS. 4A and 4B are perspective views for explaining an operation of acarrying-out mechanism of the laser processing apparatus depicted inFIG. 1;

FIGS. 5A to 5C are schematic views for explaining an operation of aperiphery detecting section of the laser processing apparatus depictedin FIG. 1;

FIGS. 6A and 6B are plan views for explaining a calculation method forcalculating a deviation amount of a wafer on a temporary placing tableby the periphery detecting section depicted in FIGS. 5A and 5B;

FIGS. 7A and 7B are perspective views for explaining an operation of acarrying mechanism of the laser processing apparatus depicted in FIG. 1;

FIGS. 8A and 8B are plan views for explaining an operation of correctingthe position of a notch in the wafer held on the chuck table;

FIG. 9 is a perspective view for explaining an operation of carrying outa processed wafer from the chuck table and holding the wafer on thetemporary placing table, by the carrying-out mechanism; and

FIG. 10 is a perspective view for explaining an operation ofaccommodating the processed wafer into a processed workpiece cassette bythe carrying-out mechanism.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferable embodiment of a laser processing apparatus configuredaccording to the present invention will be described in detail below,referring to the attached drawings. FIG. 1 depicts a perspective view ofone embodiment of the laser processing apparatus configured according tothe present invention. The laser processing apparatus 1 in theembodiment illustrated includes a stationary base 2, a holding tablemechanism 3 which is disposed on the stationary base 2 and holds aworkpiece, and laser beam applying means 4 for applying laser processingto the workpiece held by the holding table mechanism 3.

Main components of the laser processing apparatus 1 described in FIG. 1will be described while referring to FIG. 2 which separately illustratesthe main components. The holding table mechanism 3 includes a pair ofY-axis guide rails 31 disposed on the stationary base 2 in parallel toeach other along a Y-axis direction indicated by arrow Y, an X-axistable 32 disposed on the Y-axis guide rails 31 so as to be movable inthe Y-axis direction indicated by arrow Y, a pair of X-axis guide rails322 disposed on an upper surface of the X-axis table 32 in parallel toeach other along an X-axis direction indicated by arrow X, a moving base33 disposed on the X-axis guide rails 322 so as to be movable in theX-axis direction indicated by arrow X, a chuck table 34 supported on themoving base 33, a suction chuck 35 that forms an upper surface of thechuck table 34 and is formed from a gas-permeable porous ceramic, Y-axisdirection moving means 36 for moving the X-axis table 32 in the Y-axisdirection along the Y-axis guide rails 31, and X-axis direction movingmeans 37 for moving the moving base 33 in the X-axis direction along theX-axis guide rails 322. Note that suction chuck 35 is connected to asuction pump (not depicted), and is configured to be able to suctionhold a workpiece placed on an upper surface thereof.

The Y-axis direction moving means 36 includes a Y-axis linear rail 361disposed between the two Y-axis guide rails 31 and extending in theY-axis direction, and a Y-axis coil movable element 362 fitted to theY-axis linear rail 361 in a movable manner and mounted to a lowersurface of the X-axis table 32. The Y-axis linear rail 361 has aconfiguration in which, for example, N poles and S poles of a pluralityof cylindrical permanent magnets are alternately joined to form ashaft-shaped body, and the plurality of cylindrical permanent magnetsthus formed into the shaft-shaped body are disposed in a hollowcylindrical case formed of a non-magnetic material of stainless steel.Support members 363 as depicted in FIG. 2 (in FIGS. 1 and 2, only one ofthem is illustrated) are mounted to both end portions of the Y-axislinear rail 361 configured in this way, and the Y-axis linear rail 361is attached to an upper surface of the support base 2 through thesupport members 363. The Y-axis direction moving means 36 including theY-axis linear rail 361 and the Y-axis coil movable element 362constitutes a so-called linear shaft motor serving as a drive source.When a current flows in the Y-axis coil movable element 362, anattracting force and a repelling force due to magnetic forces arerepeatedly generated, whereby a thrust is generated. Therefore, thedirection in which the Y-axis coil movable element 362 is moved alongthe Y-axis linear rail 361 can be changed by changing the direction ofthe current applied to the Y-axis coil movable element 362. Such amovement in the Y-axis direction is to move in a so-called indexing feeddirection orthogonal to a processing feed direction of the chuck table34, and acts as an indexing feeding mechanism.

The X-axis direction moving means 37 is configured in substantially thesame manner as the Y-axis direction moving means 36, as a drive sourcefor moving the moving base 33 in the X-axis direction. The X-axisdirection moving means 37 includes an X-axis linear rail 371 which isdisposed between the two X-axis guide rails 322 for guiding the movingbase 33 in the X-axis direction and extends in the X-axis direction, andan X-axis coil movable element 372 fitted to the X-axis linear rail 371in a movable manner and mounted to a lower surface of the moving base33. The X-axis linear rail 371 has a configuration in which, forexample, N poles and S poles of a plurality of cylindrical permanentmagnets are alternately joined to form a shaft-shaped body, and theplurality of cylindrical permanent magnets thus formed into theshaft-shaped body are disposed in a hollow cylindrical case formed of anon-magnetic material of stainless steel. Support members 373 aremounted to both end portions of the X-axis linear rail 371 configured inthis way, as depicted in FIG. 2, and the X-axis linear rail 371 isattached to an upper surface of the X-axis table 32 through the supportmembers 373. The X-axis direction moving means 37 including the X-axislinear rail 371 and the X-axis coil movable element 372 constitutes aso-called linear shaft motor similarly to the Y-axis direction movingmeans 36. When a current flows in the X-axis coil movable element 372,an attracting force and a repelling force due to magnetic forces arerepeatedly generated, whereby a thrust is generated. Accordingly, thedirection in which the X-axis coil movable element 372 is moved alongthe X-axis linear rail 371 can be changed by changing the direction ofthe current applied to the X-axis coil movable element 372. Such amovement in the X-axis direction is to move in a so-called processingfeed direction of the chuck table 34, and acts as a processing feedingmechanism.

Referring to FIG. 3, the moving base 33 and the chuck table 34 supportedon the moving base 33 will be described more specifically. In FIG. 3,the chuck table 34 fitted to the moving base 33 is illustrated in aseparated state and as viewed from an oblique lower side. The chucktable 34 is formed from a lightweight ceramic, whereas the moving base33 is formed from a carbon fiber-reinforced plastic (CFRP). The CFRP isformed to have a specific gravity of approximately 1.5 to 2.0, whichvaries to a certain extent depending on a molding method. The CFRP is anextremely lightweight blank material as compared to those formed of ametal such as stainless steel (specific gravity: 7.9), and is excellentin strength.

As illustrated in FIG. 3, a circular recess 331 is formed in the centerof an upper surface of the moving base 33, and a bottomed hollowcylindrical member 332 is rotatably fitted or inserted in the recess331. The hollow cylindrical member 332 is formed in a bottom portion 333thereof with gas suction holes 334 and 335. The gas suction hole 334formed in the center is connected to a ventilating hole 34 b, formed inthe center of a circular projection 34 a formed at a lower surface ofthe chuck table 34, when the circular projection 34 a is fitted orinserted in the hollow cylindrical member 332. Further, the gas suctionhole 335 is formed to suction hole the chuck table 34 when the chucktable 34 is fitted or inserted in the hollow cylindrical member 332. Thechuck table 34 to be placed on the moving base 33 is configured to befreely rotatable in the directions indicated by arrows in the figure,together with rotation of the hollow cylindrical member 332.

Returning to FIG. 2, for the laser beam applying means 4, a generallyknown configuration may be adopted. The laser beam applying means 4includes a laser beam oscillator, an attenuator for output adjustment, agalvanometer scanner for adjusting the laser beam applying direction, areflective mirror, a focusing lens included in the focusing unit 4 a,etc. (omitted in illustration). Imaging means 43 is for detecting aregion to be processed of a workpiece held by the chuck table 34. Theimaging means 43 includes an optical system constituting a microscope,and an imaging element (charge-coupled device (CCD)), and is configuredto be able to send an image signal obtained by imaging to control meansand to display an image on display means (not depicted). Note that thecontrol means is composed of a computer, and includes a centralprocessing unit (CPU) for arithmetic processing according to a controlprogram, a read only memory (ROM) for storing the control program andthe like, a random access memory (RAM) capable of reading/writing fortentatively storing detected values, calculation results, etc., an inputinterface, and an output interface (omitted in illustration).

As depicted in FIGS. 1 and 2, temporary placing means 5 is disposed onan upper surface of the stationary base 2 at a position in the Y-axisdirection in relation to the X-axis table 32 on which the chuck table 34is disposed in a slidable manner. The temporary placing means 5 includesa rotatable temporary placing table 51, and a periphery detectingsection 52 for detecting a periphery of a workpiece temporarily placedon the temporary placing table 51. As depicted in FIG. 2, the peripherydetecting section 52 is provided with an opening 52 a opening laterallyat the height of the temporary placing table 51, and a light emittingelement is provided on the upper side of the opening 52, whereas a lightreceiving element is provided at that position on the lower side of theopening 52 which is opposed to the light emitting element (details willbe described later). Further, the periphery detecting section 52 isconfigured to be movable in the directions indicated by arrows in thefigure, namely, in the directions for moving toward and away from thetemporary placing table 51 by a driving mechanism disposed inside thestationary base 2. Note that the temporary placing table 51 includes atransparent resin plate, and rotational angle of the temporary placingtable 51 is detected by a rotational angle sensor (not depicted).

In the laser processing apparatus 1 in the present embodiment, asdepicted in FIG. 2, carrying-out means 6 is provided at a position whichis adjacent, in the X-axis direction, to a region in which the temporaryplacing means 5 and the holding table mechanism 3 are disposed on thestationary base 2. The carrying-out means 6 is provided with acarrying-out mechanism mount base 60, a carrying-out mechanism 61, andcarrying-out mechanism moving means 62 for moving the carrying-outmechanism 61 in the Y-axis direction.

The carrying-out mechanism 61 includes a carrying-out moving base 611, ahollow cylindrical member 612 advanced and retracted in the verticaldirection by an air cylinder incorporated in the carrying-out movingbase 611, a flat plate-shaped first arm section 613 a one end portion ofwhich is rotatably connected to an upper end portion of the hollowcylindrical member 612, a second arm section 613 b one end portion ofwhich is rotatably connected to the other end portion of the first armsection 613 a, and a robot hand 614 connected to the other end portionof the second arm section 613 b. A lower surface of the robot hand 614is formed with a plurality of suction holes (omitted in illustration),which are connected to a suction source through the hollow cylindricalmember 612 and the first and second arm sections 613 a and 613 b, sothat sucking the workpiece and letting off the workpiece can beperformed by controlling the operation/non-operation of the suctionsource. Note that the robot hand 614 can perform an action for invertingupside down through a support portion at the other end portion on thesecond arm section 613 b side, whereby its surface formed with thesuction holes can be directed to the upper side.

The carrying-out mechanism moving means 62 is configured substantiallythe same manner as the aforementioned Y-axis direction moving means 36and X-axis direction moving means 37. The carrying-out mechanism movingmeans 62 includes two carrying-out guide rails 621 disposed on an uppersurface of the carrying-out mechanism mount base 60 in the Y-axisdirection, a linear rail 622 which is disposed between the carrying-outguide rails 621 and extends in the Y-axis direction, and a coil movableelement 623 fitted to the linear rail 622 in a movable manner andmounted to a lower surface of the carrying-out moving base 611. Thelinear rail 622 is configured in the same manner as the Y-axis linearrail 361 and the X-axis linear rail 371 which constitute the Y-axisdirection moving means 36 and the X-axis direction moving means 37,respectively. Support members 624 are mounted to both end portions ofthe linear rail 622, and the linear rail 622 is attached to an uppersurface of the carrying-out mechanism mount base 60 through the supportmembers 624. The carrying-out mechanism moving means 62 including thelinear rail 622 and the coil movable element 623 constitutes a so-calledlinear shaft motor. When a current flows in the coil movable element623, an attracting force and a repelling force due to magnetic forcesare repeatedly generated, whereby a thrust is generated. Therefore, thedirection in which the coil movable element 623 is moved along thelinear rail 622 can be changed by changing the direction of the currentapplied to the coil movable element 623.

A housing 40 incorporating laser beam applying means 4 is providedadjacently to the stationary base 2, in such a manner as to be along theX-axis table 32 disposed on the stationary base 2. The housing 40includes a vertical wall section 41 extending vertically upward from afloor surface, and a horizontal wall section 42 extending horizontallyfrom an upper end of the vertical wall section 41. As depicted in FIG.1, carrying means 8, the imaging means 43, and the focusing unit 4 a ofthe laser beam applying means 4 are disposed, in the state of beingaligned in the X-axis direction, on a lower surface of a tip portion ofthe horizontal wall section 42.

As depicted in the figure, a cassette placing mechanism 7 is disposed insuch a manner that the carrying-out means 6 is located between thestationary base 2 and the cassette placing mechanism 7 in the X-axisdirection of the stationary base 2. The cassette placing mechanism 7 isprovided with an unprocessed workpiece cassette 72 a in which toaccommodate unprocessed workpieces, a processed workpiece cassette 72 bin which to accommodate processed workpieces, and a cassette table 71 onwhich the unprocessed workpiece cassette 72 a and the processedworkpiece cassette 72 b are disposed in the state of being aligned inthe Y-axis direction. It is preferable that the unprocessed workpiececassette 72 a is disposed at a position near the temporary placing means5, whereas the processed workpiece cassette 72 b is disposed on the sidenear the receiving position of the chuck table 34, as depicted in thefigure. Note that the “receiving position” of the chuck table 34 refersto a position with which the center of the chuck table 34 coincides on astraight line drawn in the Y-axis direction from the center of thetemporary placing table 51 when the chuck table 34 is moved in theX-axis direction on the X-axis table 32.

As depicted in FIG. 1, the carrying means 8 that sucks the workpiece onthe temporary placing table 51 and carries the workpiece onto the chucktable 34 located at the receiving position is provided on the lowersurface of the horizontal wall section 42 of the housing 40. In FIG. 2,the carrying means 8 is illustrated on the upper side in the state ofbeing separated from the horizontal wall section 42. Describing morespecifically based on the figure, the carrying means 8 includes a casing81 incorporating a known belt mechanism therein, an opening 82 openingin a side wall of the casing 81 in a longitudinal direction, a carryingarm 83 which is supported by the belt mechanism incorporated in thecasing 81 and extends to the outside from the opening 82, a rod 84mounted to a tip portion of the carrying arm 83 in such a manner that itcan be advanced and retracted in regard of a downward direction, and asucker pad 85 supported by a tip portion of the rod 84. The sucker pad85 is formed with a plurality of suction holes on the lower surface side(not depicted), and is connected to a suction source (not depicted)through the rod 84 and the carrying arm 83 so that a workpiece can besucked or let off by the lower surface side of the sucker pad 85.

The laser processing apparatus 1 configured according to the presentinvention generally has the above-mentioned configuration, and itsoperation will be described based on FIGS. 4A to 10. Note that in FIGS.4A and 10, the housing 40 is omitted for convenience of explanation.

In performing laser processing by the laser processing apparatus 1 inthe present embodiment, an operator places on the cassette table 71 ofthe cassette placing mechanism 7 the unprocessed workpiece cassette 72 ain which unprocessed workpieces (in the present embodiment, siliconwafers W) are accommodated, and the processed workpiece cassette 72 bwhich is prepared in an empty state for accommodating the processedwafers W. Note that the laser processing apparatus 1 in the presentembodiment is for performing laser processing consisting in applying alaser beam of such a wavelength as to be transmitted through the wafer Wto the wafer W so as thereby to form a modified layer inside the waferW. The wafers W, each with a protective tape adhered to its frontsurface side on which devices are formed, are accommodated in theunprocessed workpiece cassette 72 a at predetermined intervals, withtheir front surface side up.

When the start of laser processing is commanded to the laser processingapparatus 1 by the operator, first, the carrying-out mechanism movingmeans 62 is operated to position the carrying-out moving base 611 of thecarrying-out mechanism 61 in front of the unprocessed workpiece cassette72 a. When the carrying-out mechanism 61 has been positioned in front ofthe unprocessed workpiece cassette 72 a, the robot hand 614 is advancedinto the unprocessed workpiece cassette 72 a in order to carry out anunprocessed wafer W accommodated in the unprocessed workpiece cassette72 a, as depicted in FIG. 4A. In this instance, the surface formed withthe suction holes of the robot hand 614 is directed to the upper side.In the unprocessed workpiece cassette 72 a, a plurality of unprocessedwafers W are accommodated in a horizontal state and at predeterminedvertical intervals. The robot hand 614 is advanced to the lower surfaceside of a predetermined wafer W in a state in which the robot hand'ssurface formed with the suction holes is directed up, and the backsurface side of the unprocessed wafer W is sucked from below.

When the back surface of the unprocessed wafer W is sucked by thesuction hole-formed surface of the robot hand 614 inside the unprocessedworkpiece cassette 72 a, the first arm 613 a and the second arm 613 bare rotated appropriately to thereby take out the unprocessed wafer Wfrom the unprocessed workpiece cassette 72 a, and, as depicted in FIG.4B, the wafer W sucked by the robot hand 614 is moved toward thetemporary placing table 51. During this operation, the robot hand 614 isrotated in such a manner that the suction hole-formed surface thereof isdirected downward, namely, that the surface holding the wafer W thereonis directed downward. After the movement onto the temporary placingtable 51, the hollow cylindrical member 612 is lowered to thereby bringthe wafer W into contact with the upper surface of the temporary placingtable 51, and the operation of the suction source is stopped, to releasethe sucked state. Note that as depicted in FIG. 4A, the temporaryplacing table 51 is also provided in its center with a suction holeconnected to the suction source, so that when suction through thesuction hole 51 a on the temporary placing table 51 side is conductedsimultaneously with the releasing of the sucked state on the robot hand614 side, the wafer W can be smoothly sucked onto the temporary placingtable 51. In this way, the unprocessed wafer W is held on the temporaryplacing table 51, with its back surface side up.

When the unprocessed wafer W is suction held on the temporary placingtable 51, the periphery detecting section 52 is operated to perform aperiphery detecting step of detecting the peripheral portion of thewafer W and the position of a notch N indicative of the crystalorientation of the wafer W. The periphery detecting step will bedescribed more specifically. As depicted in FIG. 5A, at the time ofplacing the wafer W on the temporary placing table 51, the peripherydetecting section 52 has been moved into a retracted position of beingspaced from the temporary placing table 51 such as not to contact thewafer W. After the wafer W is placed on the temporary placing table 51,driving means (not depicted) is operated to move the periphery detectingsection 52 to the temporary placing table 51 side, to let a peripheralportion of the temporary placing table 51 advance into the opening 52 a,as depicted in FIG. 5B. In this instance, the size (diameter) of thewafer W to be processed is preliminarily registered in control means(not depicted), and a periphery position of the wafer W is positionedsubstantially at the center of the opening 52 a, as depicted in FIG. 5C.As illustrated in the figure, a light emitting element 521 having apredetermined length in the left-right direction in the figure isdisposed on the upper side of the opening 52 a, and a light receivingelement 522, for example, a line sensor, is disposed on the lower sideof the opening 52 a at a position opposed to the light emitting element521. The operation of the periphery detecting section 52 will bedescribed more.

In the case where the wafer W on the temporary placing table 51 iscarried onto the chuck table 34 located at the above-mentioned receivingposition by use of the carrying means 8, the center position of thewafer W must be situated on the Y-axis line passing through the centerof the chuck table 34. However, when the unprocessed wafer W is placedonto the temporary placing table 51 by the aforementioned carrying-outmeans 6, it is difficult to place the wafer W such that the centerposition of the wafer W coincides accurately with the center position ofthe temporary placing table 51. When the wafer W whose center positionis deviated on the temporary placing table 51 is carried from thetemporary placing table 51 onto the chuck table 34 by the carrying means8 in the deviated state, a deviation results between the center of thechuck table 34 and the center of the wafer W. In view of this, in thepresent embodiment, the periphery of the wafer W and the position of thenotch N indicative of the crystal orientation of the wafer W aredetected by use of the periphery detecting section 52, whereby thecenter position of the wafer W suction held on the temporary placingtable 51 and the direction in which the notch N is positioned aregrasped. The detection method will be described below.

In the state as depicted in FIG. 5C, the light emitting element 521 andthe light receiving element 522 are operated, and the temporary placingtable 51 is rotated in the direction indicated in FIG. 5B by use ofdriving means (not depicted). As aforementioned, the temporary placingtable 51 includes a transparent plate, and the rotational positionthereof has been detected. Therefore, a region where light radiated fromthe light emitting element 521 is shielded by the wafer W and a regionwhere the wafer W is absent and the light is not shielded but reachesthe light receiving element 522 are distinguished from each other, andan outer edge shape of the wafer W on the temporary placing table 51 isdetected in correspondence with the rotational angle of the temporaryplacing table 51. In addition, with the outer edge shape of the wafer Wthus grasped, the notch N indicative of the crystal orientation of thewafer W can also be detected.

Referring to FIGS. 6A and 6B, a method of calculating the positionaldeviation amount of the wafer W relative to the temporary placing table51 and the angle thereof will be described. As depicted in FIG. 6A, whenthe outer edge shape of the wafer W is detected in correspondence withthe rotational angle of the wafer W by the aforementioned peripherydetecting section 52, a minimum dmin of the distance of the outer edgeshape from an outer edge of the temporary placing table 51 preliminarilystored and a maximum dmax of the distance are grasped together with therotational angle position. In addition, when a straight line L1(indicated by alternate long and short dash line) connecting thepositions where the minimum dmin and the maximum dmax are obtained isspecified, to what extent a center O1 of the wafer W is deviated towardthe dmin side from a center O2 of the temporary placing table 51 isgrasped from the following expression (1), since the straight line L1necessarily pass the center O1 of the wafer W and the center O2 of thetemporary placing table 51 whose position is preliminarily specified.[dmax−dmin]/2=deviation amount  (1)

For example, where the maximum dmax in the present embodiment is 8 mmand the minimum dmin is 2 mm, it is gasped from calculation of thedeviation amount based on the above expression (1) that the center O1 ofthe wafer W is deviated by 3 mm toward the minimum dmin side from thecenter O2 of the temporary placing table 51. In addition, when thestraight line L1 is detected by the periphery detecting section 52, aninclination angle θ1 of the straight line L1 relative to the Y-axisdirection (indicated by a dotted line P) is grasped, and the position ofthe notch N is also grasped. Therefore, an angle θ2 between a straightline L2 (indicated by alternate long and two short dashes line)connecting the center of the wafer W and the notch N and the straightline L1 is also grasped. The position of the wafer W, the deviationamount, and the angle as above are stored in the memory of the controlmeans (not depicted).

When the deviation amount (3 mm) of the position of the wafer W on thetemporary placing table 51 and the direction (θ1) thereof have beengrasped as aforementioned, the temporary placing table 51 is rotated byθ1, as depicted in FIG. 6B, to cause the straight line L1 and thestraight line P indicative of the Y-axis direction to coincide with eachother. As a result, the center O1 of the wafer W and the center O2 ofthe temporary placing table 51 are aligned in the Y-axis direction, andthe center O1 of the wafer W is deviated by 3 mm in the Y-axis directionfrom the center O2 of the temporary placing table 51. It is grasped,simultaneously with this, that the inclination angle of the notch Nrelative to the Y-axis direction (straight line P) is θ2.

When the temporary placing table 51 has been rotated by θ1, a carryingstep of carrying the wafer W onto the chuck table 34 is then conductedby use of the carrying means 8. As depicted in FIG. 7A, the carrying arm83 of the carrying means 8 is operated by driving means (not depicted)to position the sucker pad 85 into a position on the upper side of thetemporary placing table 51, the rod 84 is extended and lowered, to bringthe sucker pad 85 into contact with the wafer W, and the suction source(not depicted) is operated so that the wafer W is sucked by the suckerpad 85. In this instance, since the sucker pad 85 is so set that itscenter always coincides with the center O2 of the temporary placingtable 51, the wafer W is sucked by the sucker pad 85 in a state in whichthe center O1 of the wafer W is deviated by 3 mm in the Y-axis directionfrom the center of the sucker pad 85.

When the wafer W has been sucked by the sucker pad 85, the rod 84 isshrunk to raise the sucker pad 85, and the carrying arm 83 as isdirectly moved in the Y-axis direction, as depicted in FIG. 7B. In thisinstance, the chuck table 34 is positioned in a position at which itscenter is aligned with the center O2 of the temporary placing table 51in the Y-axis direction, that is, positioned in the receiving position,so that by moving the carrying arm 83 in the Y-axis direction by aprescribed amount, it is possible to cause the center of the sucker pad85 and the center of the chuck table 34 located in the receivingposition to coincide with each other. Here, since it is grasped that thewafer W sucked onto the sucker pad 85 sucked in the state of beingdeviated by 3 mm in the Y-axis direction and this is stored in thecontrol means, as aforementioned, the moving amount is corrected by 3 mmat the time of carrying the wafer W by the carrying arm 83. In otherwords, a distance smaller than the prescribed amount by 3 mm is themoving amount for the carrying arm 83. Then, the carrying arm 83 ismoved by the distance corrected in relation to the prescribed amount, asdepicted in FIG. 7B, whereon the wafer W is positioned in a positionwhere the center of the wafer W and the center of the chuck table 34coincide with each other in plan view, so that by extending the rod 84to lower the sucker pad 85, the wafer W is placed on the chuck table 34in a state where their centers coincide with each other. When the waferW has been placed on the chuck table 34, the operation of the suctionmeans on the sucker pad 85 ide is stopped, whereas the suction means foracting on the suction chuck 35 forming the holding surface of the chucktable 34 is operated, to suction hold the wafer W. Note that in thisinstance, the wafer W is placed on the chuck table 34 in a state inwhich its front surface side on which the devices are formed is placedon the chuck table 34, with a protective tape (not depicted)therebetween.

As depicted in FIG. 8A, according to the aforementioned carrying means8, the wafer W is placed on the chuck table 34 with its center O1positioned accurately on a center O3 of the chuck table 34. In thisstate, however, the position of the notch N in the wafer W is deviatedby the angle θ2 in relation to the prescribed direction indicated by thedotted line P, as indicated by the straight line L2. As aforementioned,the θ2 has been detected by the periphery detecting section 52 in thestate where the wafer W is placed on the temporary placing table 51 andbeen stored in the memory of the control means. Therefore, whilereferring to the value of θ2 stored in the control means, the chucktable 34 is moved by θ2 to thereby move the notch N into a prescribedposition, as depicted in FIG. 8B. As a result, the position of the notchN is corrected, and the crystal orientation of the wafer W is positionedin a predetermined direction suitable for laser processing.

Through the above-mentioned steps, the wafer W is correctly placed onthe chuck table 34, and, by moving the chuck table 34 to a positionunder the imaging means 43 and the focusing unit 4 a of the laser beamapplying means 4 illustrated in FIG. 1, a laser processing step can becarried out. In performing the laser processing step, first, so-calledalignment is conducted in which a processing region of the wafer W to beprocessed is imaged by the imaging means 43 and positional matchingbetween the focusing unit 4 a and the processing region is performed.Then, laser processing is conducted by applying a pulsed laser beamwhile relatively moving the focusing unit 4 a and the processing regionof the wafer W by operating the aforementioned Y-axis direction movingmeans 36 and X-axis direction moving means 37. Note that, for example,for enabling alignment from the back side of the wafer W formed ofsilicon, the imaging means 43 in the present embodiment includes a lightsource for radiating infrared rays able to be permitted through siliconfrom the back side of the wafer W, an optical system for catching theinfrared rays, an imaging element (infrared CCD) for outputting anelectrical signal corresponding to the infrared rays, etc.

As laser processing conditions in the present embodiment, for example,the following processing conditions may be selected.

Wavelength of laser beam: 1064 nm

Repetition frequency: 10 kHz

Average output: 1.0 W

Processing feed velocity: 2,000 mm/second

By this operation, a modified layer is formed inside the wafer W alongdivision lines for dividing the wafer W. Here, an operational advantageof the case of using the moving base 33 formed from carbonfiber-reinforced plastic (CRFP) based on the present invention will bespecifically described below, comparing the case of a conventionalmoving base formed from stainless steel.

First, in comparing the moving base 33 of the present invention and theconventional moving base, the laser processing apparatus 1 in thepresent embodiment is used, and the other configurations than the movingbase are assumed to be the same. In the case of performing laserprocessing in the laser processing apparatus 1, the moving base 33placed on the X-axis guide rails 322 is accelerated at a predetermineddistance from the receiving position, and is put in uniform motion inthe processing region. Assuming the weight of the conventional movingbase is m, the weight of the moving base of the present invention ism/4. An acceleration for reaching a constant velocity at a predetermineddistance in the case of the conventional moving base is assumed to bea₁, whereas an acceleration for reaching a constant velocity at thepredetermined distance in the case of the moving base of the presentinvention is assumed to be a₂. Since the laser processing apparatus isthe same in both cases, assuming that an inertial force F₁ in moving themoving base 33 of the present invention and an inertial force F₂ inmoving the conventional moving base are the same, a relation:F ₁ =a ₁ ·m=F ₂ =a ₂·(m/4)exists, and, therefore, an equation:a ₁ =a ₂/4  (1)is obtained.

Since the predetermined distance at which a constant velocity is reachedby both the moving bases is the same, let a time at which theconventional moving base reaches a constant velocity be t₁, and let atime at which the moving base 33 of the present invention reaches aconstant velocity be t₂, then an equation:∫₀ ^(t) ¹ a ₁ ·tdt=∫ ₀ ^(t) ² z ₂ ·tdtis established. From this equation, an equation:(a ₁/2)·t ₁ ²=(a ₂/2)·t ₂ ²is deduced, and, by putting the equation (1) into this equation, arelation:t ₂ =t ₁/2  (2)is obtained.

Assuming that a velocity that can be reached at the predetermineddistance is V₁ for the conventional moving base and is V₂ for the movingbase 33 of the present invention, following equations:V ₁ =a ₁ ·t ₁  (3)V ₂ =a ₂ ·t ₂  (4)are established. From the equations (1) to (4), a following equation:V ₂=2a ₁ ·t ₁  (5)is deduced. Assuming that the velocity V₁ which can be reached by theconventional moving base is 1,000 mm/second, then, since the followingrelation:a ₁ ·t ₁=1,000 [mm/second]is deduced from the equation (3), a velocity ofV ₂=2,000 [mm/second]can be reached by the moving base 33 of the present invention.

Note that the laser processing step in the present embodiment is a knowntechnology, and does not constitute an essential part of the presentinvention, and, therefore, a detailed description thereof is omitted.

The laser processing apparatus 1 in the present embodiment has theconfiguration as described above. Therefore, while laser processing isconducted after the wafer W is carried onto the chuck table 34 by use ofthe carrying means 8, it is possible carry out a new unprocessed wafer Wfrom the unprocessed workpiece cassette 72 a by operating thecarrying-out means 6 and to cause the wafer W to be placed and held onthe temporary placing table 51, as depicted in FIG. 7B. In other words,after the wafer W is carried from the temporary placing table 51, thecarrying-out means 6 is immediately operated to perform an operation asdepicted in FIGS. 4A and 4B, whereby the new wafer W can be placed onthe temporary placing table 51 and be suction held there. Then, whilethe wafer W formerly carried onto the chuck table 34 is undergoing laserprocessing, the periphery detecting section 52 can be operated to detectthe deviation amount of the position of the new wafer W held on thetemporary placing table 51, the direction thereof and the position ofthe notch N, and the deviated direction thereof can be preliminarilycorrected by rotating the temporary placing table 51, as required.

The wafer W formerly carried onto the chuck table 34 and subjected tolaser processing is moved into the receiving position of the chuck table34 together with the chuck table 34. When the chuck table 34 has beenmoved into the receiving position, as depicted in FIG. 9, thecarrying-out mechanism 61 of the carrying-out means 6 is moved on thecarrying-out guide rails 621 by operating the carrying-out mechanismmoving means 62, and is positioned in the vicinity of the receivingposition. When the carrying-out mechanism 61 has been moved into thevicinity of the receiving position, the hollow cylindrical member 612,the first arm 613 a, the second arm 613 b, and the robot hand 614 areoperated to suck the processed wafer W on the chuck table 34 on thelower surface side of the robot hand 614, as depicted in the figure.

When the processed wafer W has been sucked by operating the robot hand614, the first arm 613 a, the second arm 613 b, and the hollowcylindrical member 612 are further operated to accommodate the processedwafer W into a predetermined position in the processed workpiececassette 72 b, as depicted in FIG. 10. Note that after the processedwafer W is sucked at the chuck table 34, the robot hand 614 is rotatedsuch that the processed wafer W is accommodated in the cassette 72 b,with its device-formed surface side up and with its back surface sidedown. Note that the present invention is not restricted to this mode ofoperation. A mode may be adopted in which the unprocessed wafers W arepreliminarily accommodated in the unprocessed workpiece cassette 72 awith their back surface side directed up, the back surface side of thewafer W is sucked by the robot hand 614 from above and is carried,whereas the processed wafer W on the chuck table 34 is sucked by therobot hand 614, after which the processed wafer W is accommodated intothe processed workpiece cassette 72 b, with its back surface side keptup, without rotating the robot hand 614.

After the wafer W is carried out from the chuck table 34 by thecarrying-out mechanism 61, the carrying means 8 can be operated to carrythe wafer, which is held on the temporary placing table 51 and is to beprocessed next, onto the chuck table 34, and correction of the directionof the notch N and the laser processing step can be performed, asdescribed above referring to FIGS. 8A and 8B. In other words, in thelaser processing apparatus configured based on the present invention,the processed wafer W can be accommodated into the processed workpiececassette 72 b in a direct manner, without passing through the routealong which the unprocessed wafer W is carried. Therefore, the route ofthe unprocessed wafer W and the route of the processed wafer W do notoverlap each other, so that the wafers W can be processed efficiently.

The present invention is not restricted to the above-describedembodiment, and various modifications can be assumed. For example, whilethe temporary placing table 51 of the temporary placing means 5 has beencomposed of a transparent plate and the periphery position of the waferW has been detected by the light emitting element 521 and the lightreceiving element 522 disposed in the periphery detecting section 52 inthe present embodiment, this is not restrictive. In the case where thetemporary placing table 51 is not composed of a transparent plate, aconfiguration may be adopted in which a laser beam is radiated downwardon the upper side of the opening 52 a of the periphery detecting section52, and the reflected laser beam is received, to thereby detectruggedness (projections and recesses) on the temporary placing table anddetect the periphery position. Alternatively, a configuration may beadopted in which the ruggedness on the temporary placing table isdetected by use of a known ultrasonic-wave or infrared-ray technique,thereby detecting the periphery position. Further, a configuration maybe adopted in which the outside diameter shape is recognized by suchmeans as image recognition processing.

While the unprocessed workpiece cassette 72 a and the processedworkpiece cassette 72 b have been prepared in the present embodiment,the present invention is not restricted to this configuration. Aconfiguration may be adopted in which only one cassette is prepared, andthe processed wafer W is returned into a predetermined position in thecassette in which the wafer W has been accommodated before processing.

While a case of laser processing in which a laser beam of such awavelength as to be transmitted through the wafer W is applied to thewafer W to form a modified layer inside the wafer has been described inthe present embodiment, this is not restrictive of the presentinvention. The present invention is also applicable to a laserprocessing apparatus for performing so-called ablation processing byapplying to the wafer W a laser beam of such a wavelength as to beabsorbed in the wafer W. The present invention is applicable to laserprocessing apparatuses, irrespectively of the kind of the laserprocessing.

While an example in which the Y-axis direction moving means 36, theX-axis direction moving means 37, and the carrying-out mechanism movingmeans 62 are driven by the so-called linear shaft motor has beenexplained in the present embodiment, this is not restrictive of thepresent invention. A mechanism in which a so-called ball screw isrotated by a motor to convert a rotational motion of the motor into arectilinear motion can be used as a drive source for each of theaforementioned driving means.

In the present embodiment, a configuration has been adopted in which theperiphery detecting section 52 is provided with the opening 52 a, andthe periphery detecting section 52 is movable in the direction of thetemporary placing table 51, such that the periphery of the wafer Wplaced on the temporary placing table 51 can be situated between theelements of the periphery detecting section 52. However, it is assumedthat the wafers W to be processed by the laser processing apparatus 1may vary in size, and the periphery position of the wafer W may not beconstant. In view of this, the position at which the wafer W is situatedbetween the light emitting and light receiving elements on the upper andlower sides of the opening 52 a may be moved, as required, according tothe size of the wafer W to be processed. Besides, as required, theperiphery detecting section 52 may be replaced so as to cope withdifferences in the size of the wafer W.

The present invention is not limited to the details of the abovedescribed preferred embodiment. The scope of the invention is defined bythe appended claim and all changes and modifications as fall within theequivalence of the scope of the claim are therefore to be embraced bythe invention.

What is claimed is:
 1. A laser processing apparatus for processing aplate-shaped workpiece by applying a laser beam to the workpiece, thelaser processing apparatus comprising: a cassette table for placingthereon a cassette in which a plurality of workpieces are accommodated;carrying-out means for carrying out the workpiece from the cassetteplaced on the cassette table; temporary placing means for temporarilyplacing the workpiece carried out by the carrying-out means; carryingmeans for carrying the workpiece from the temporary placing means to achuck table; a moving base for supporting the chuck table; imaging meansfor detecting a region to be processed of the workpiece held on thechuck table; X-axis direction moving means for moving the chuck table inan X-axis direction; Y-axis direction moving means for moving of thechuck table in a Y-axis direction orthogonal to the X-axis direction;and laser beam applying means for applying a laser beam to the workpieceheld on the chuck table, wherein the moving base is formed from a carbonfiber-reinforced plastic.
 2. The laser processing apparatus as definedin claim 1, wherein the X-axis direction moving means includes an X-axistable having an X-axis guide rail for guiding the moving base in theX-axis direction, and a drive source for moving the moving base, and theY-axis direction moving means includes a Y-axis guide rail for guidingthe X-axis table in the Y-axis direction, and a drive source for movingthe X-axis table.
 3. The laser processing apparatus as defined in claim1, wherein the carbon fiber-reinforced plastic has a specific gravity ofapproximately 1.5 to 2.0.